Zhao Claire Y, Greenstein Joseph L, Winslow Raimond L
Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
J Mol Cell Cardiol. 2015 Nov;88:29-38. doi: 10.1016/j.yjmcc.2015.09.011. Epub 2015 Sep 23.
In cardiac myocytes, the second messenger cAMP is synthesized within the β-adrenergic signaling pathway upon sympathetic activation. It activates Protein Kinase A (PKA) mediated phosphorylation of multiple target proteins that are functionally critical to cardiac contractility. The dynamics of cAMP are also controlled indirectly by cGMP-mediated regulation of phosphodiesterase isoenzymes (PDEs). The nature of the interactions between cGMP and the PDEs, as well as between PDE isoforms, and how these ultimately transduce the cGMP signal to regulate cAMP remains unclear. To better understand this, we have developed mechanistically detailed models of PDEs 1-4, the primary cAMP-hydrolyzing PDEs in cardiac myocytes, and integrated them into a model of the β-adrenergic signaling pathway. The PDE models are based on experimental studies performed on purified PDEs which have demonstrated that cAMP and cGMP bind competitively to the cyclic nucleotide (cN)-binding domains of PDEs 1, 2, and 3, while PDE4 regulation occurs via PKA-mediated phosphorylation. Individual PDE models reproduce experimentally measured cAMP hydrolysis rates with dose-dependent cGMP regulation. The fully integrated model replicates experimentally observed whole-cell cAMP activation-response relationships and temporal dynamics upon varying degrees of β-adrenergic stimulation in cardiac myocytes. Simulations reveal that as a result of network interactions, reduction in the level of one PDE is partially compensated for by increased activation of others. PDE2 and PDE4 exert the strongest compensatory roles among all PDEs. In addition, PDE2 competes with other PDEs to bind and hydrolyze cAMP and is a strong regulator of PDE interactions. Finally, an increasing level of cGMP gradually out-competes cAMP for the catalytic sites of PDEs 1, 2, and 3, suppresses their cAMP hydrolysis rates, and results in amplified cAMP signaling. These results provide insights into how PDEs transduce cGMP signals to regulate cAMP and how PDE interactions affect cardiac β-adrenergic response.
在心肌细胞中，第二信使环磷酸腺苷（cAMP）在交感神经激活时于β-肾上腺素能信号通路中合成。它激活蛋白激酶A（PKA）介导的多种对心脏收缩功能至关重要的靶蛋白磷酸化。cAMP的动态变化也受到环磷酸鸟苷（cGMP）介导的磷酸二酯酶同工酶（PDEs）调节的间接控制。cGMP与PDEs之间以及PDE同工型之间相互作用的性质，以及这些如何最终转导cGMP信号来调节cAMP仍不清楚。为了更好地理解这一点，我们构建了心肌细胞中主要的cAMP水解PDEs（1-4）的详细机制模型，并将它们整合到β-肾上腺素能信号通路模型中。PDE模型基于对纯化的PDEs进行的实验研究，这些研究表明cAMP和cGMP竞争性结合PDEs 1、2和3的环核苷酸（cN）结合域，而PDE4的调节通过PKA介导的磷酸化发生。单个PDE模型可再现实验测量的cAMP水解速率以及剂量依赖性的cGMP调节。完全整合的模型可复制实验观察到的心肌细胞在不同程度β-肾上腺素能刺激下的全细胞cAMP激活反应关系和时间动态。模拟结果显示，由于网络相互作用，一种PDE水平的降低会被其他PDE激活增加所部分补偿。在所有PDEs中，PDE2和PDE4发挥最强的补偿作用。此外，PDE2与其他PDE竞争结合并水解cAMP，是PDE相互作用的强调节剂。最后，cGMP水平的升高逐渐在PDEs 1、2和3的催化位点上比cAMP更具竞争力，抑制它们的cAMP水解速率，并导致cAMP信号放大。这些结果为PDEs如何转导cGMP信号来调节cAMP以及PDE相互作用如何影响心脏β-肾上腺素能反应提供了见解。
